This proposal seeks to develop a strategy of genomic recombination suitable for applications in both cancer research and therapy, and is a revised resubmission of RA-CA-126664 responsive to RFA-CA-07-002. At present, there is no method for targeted and site-specific recombination of the endogenous human genome. Such `genome surgery'would enable the genetic dissection of cancer biology, as well as, empower a new approach to gene therapy. The rationale for the proposed work is that RecZFs, with their capacity for efficiently excising, inverting, or integrating large segments of DNA in many sequence contexts, are a unique and powerful tool for both introducing and repairing genetic defects related to cancer. This strategy contrasts with current gene therapies, which provide only transient gene expression or risk non-specific genomic integration of exogenous DNA. The proposed research focuses on the TP53 locus, a crucial tumor-suppressor, which is functionally inactivated in many different kinds of human cancer. The overall objective of this research proposal is to develop tools for efficient and selective integration into any genomic site, using the TP53 locus as a model target. The central hypothesis is that RecZFs, constructed from novel zinc finger proteins and evolved catalytic domains, will be able to perform this task. As powerful tools for genetic manipulation, we anticipate that RecZFs could facilitate the creation of novel animal models of cancer, the application of gene therapy, and the elucidation of cancer genetics.